The present invention generally relates to small rotary handheld power tools, and more particularly to a method and apparatus for protecting an attachment device that is mounted on such power tools.
Small handheld power tools that perform drilling, sawing and other types of cutting and the like are known in the prior art and have been widely used by hobbyists, artisans, tradesmen and others in a wide variety of applications. Such rotary hand tools generally have a motor with a rotary output shaft that extends from a nose portion that is more recently configured to connect to various accessories or attachment devices. Some of these rotary hand tools are quite powerful for their size and are used by tradesmen in the building trades as spiral saws that use a side cutting rotary tool bit to penetrate and rapidly cut holes in drywall sheets and other material. The tools are usually always provided with a mechanism for holding such tool bits and are generally in the form of a collet that fits within a bore of the power tool output shaft that has a center bore for receiving a tool bit such as the spiral saw bit and a collet nut that can tighten the collet against the tool bit that is placed in the collet. To tighten the collet nut, the output shaft desirably has a shaft lock mechanism that can be manipulated to engage the output shaft and hold it from rotating so that the user can use a wrench or the like to tighten the nut.
Such tools can also be used with an attachment device that has a right angle shaft configuration that drives a circular saw blade for making under-cuts in building trim molding and the like for installing flooring material and tile. Other right angle attachment devices may be configured to drive a grinding wheel, a sanding pad or polishing pad.
Such a right angle attachment device has an input shaft that must be interconnected with the output shaft of the tool when the attachment device is mounted on the tool. The interconnection can present problems resulting from the relatively high speed operation, which together with some slight misalignment of the two shafts, can create undesirable levels of vibration. One way to minimize such vibration is to provide a flexible interconnection between the output shaft of the power tool and the input shaft of the attachment device.
While such a flexible interconnection can significantly reduce such vibration, some embodiments of such a flexible interconnection may be damaged if it is subjected to an excessive torque.